Phase shifter

ABSTRACT

A phase shifter having two multiwinding transformers. The primary windings of the like phases of different transformers are connected in series and arranged in a three-phase system. The secondary windings of unlike phases of different transformers are interconnected and form two three-phase output voltage sets. Each transformer has control windings connected to respective switching devices. Actuation of a respective switching device provides for changing the phase angle between the three-phase output voltage sets from 0° to 120° or 180°.

The present invention relates to transformers, and more particularly tophase shifters.

The invention can most advantageously be used for controlling theoperation of power transmission systems of high power-carrying capacity.

Power transmission systems of high power-carrying capacity are normallymade up of three-phase lines. These lines are spaced as little apart ascan be tolerated from the viewpoint of phase-to-phase overvoltage. Byadjusting the phase shift or angle between the three-phase voltage setsat the entry to different lines, one can determine the amount and signof line-to-line electromagnetic influence, hence set the limit of thepower being transmitted. Symmetrical adjustment of the phase shiftbetween the threephase voltage sets at the entry to different powertransmission lines provides for the possibility to change the limit ofthe power being transmitted within a wide range without affecting thehomogeneity of the lines making up a power transmission system of highpower-carrying capacity. The advantages of power transmission systems ofhigh power-carrying capacity can be most fully realized provided theyhave means for adjusting the phase shift. The latter can be adjustedcontinuously or discretely. Continuous adjustment is an effective meansfor making full use of the adjustability of a power transmission systemof high power-carrying capacity. However, it complicates the adjustingmeans, as well as the control system, maintenance and operation.Discrete adjustment, on the other hand, is advantageous in itssimplicity, high reliability and speed. It is particularly instrumentalin the case of a clearly defined repetitive-peak load curve.

A prior art phase shifter comprises three groups of single-phasetransformers whose primary windings are connected to a three-phasenetwork. The primary windings of all the three groups are connected inseries to form three primary circuits in a star or delta arrangement.The secondary windings of the three transformers of each group are alsoconnected in series to form three secondary circuits in a star or deltaarrangement. The transformers also have two counteractive d-c biaswindings, one of these windings providing for magnetic bias while theother serves as a control winding. To make for a phase shift of ± 120°,the bias windings are provided only on two transformers, whereas thecontrol windings are provided on all three. In the initial state, thereis no current through the control winding, while flowing through themagnetic bias winding is direct current saturating the cores ofrespective transformers. As a result, in each group of primary windings,the supply voltage is applied to the primary winding of thenon-saturated transformer. In each group of secondary windings, thevoltages across the saturated transformer phases are equal to zero,while the output voltage of each group of secondary windings is equal tothe non-saturated transformer secondary voltage, both in phase and inmagnitude. In this case, the output voltage of all the three groups ofsecondary windings form a three-phase set of output voltages. As directcurrent is fed to the control winding, the transformer operating underconditions of free magnetization (non-saturated transformer) becomessaturated, while one of the saturated transformers becomesnon-saturated. The output voltage of each group of secondary windingshas its phase shifted through 120°. In the case of reversal of thedirect current through the control winding, the phase of the outputvoltage of each secondary winding group is shifted through -120°.

The above-described known phase shifter falls to provide for symmetricadjustment of the phase angle between two output voltage sets, which isrequired for the operation of power transmission systems of highpower-carrying capacity, and introduces high longitudinal resistanceinto the load circuit. In addition, the installed power of the phaseshifter is three times as high as the maximum load power.

These disadvantages substantially limit the application of the prior-artphase shifter in three-phase voltage sets in power transmission systemsof high power-carrying capacity.

It is an object of the present invention to provide a phase shiftercapable of regulating the operation of a power transmission system ofhigh power-carrying capacity by symmetrically adjusting the phase shiftbetween two three-phase voltage sets at the entry to the powertransmission system lines, the phase shifter having its installed powerreduced as well as the resistance introduced into the load circuit.

This object is attained by that in a phase shifter comprisingthree-phase multiwinding transformers each having primary windingsconnected in series, for each phase, and arranged in a three-phasesystem, secondary windings and control windings, the secondary windingsof the first transformer being connected to those of the secondtransformer, the first transformer is, according to the invention,provided with additional secondary windings to form two three-phaseoutput voltage sets, the secondary windings of the second transformerhaving their ends connected in a three-phase system, while the beginningof each secondary winding has connected thereto at least two secondarywindings of the first three-phase transformer: in addition, the controlwindings of each three-phase transformer are connected to respectiveswitching devices which short the control windings, thereby setting therequired phase angle between the three-phase output voltage sets.

It is advisable that the ends of the secondary windings of all phases ofthe second three-phase transformer be connected to a common neutralpoint, while the beginnings of the secondary winding of each phase ofthe second three-phase transformer should have connected thereto thebeginnings of the secondary windings of the other two phases of thefirst three-phase transformer.

It is also advisable that the secondary windings of the secondthree-phase transformer be delta-connected with each apex of the deltahaving connected thereto the common point of respectiveseries-aiding-connected secondary windings of the first three-phasetransformer, the phase of the voltage across the latter windingscoinciding with that of the voltage across the secondary winding of thesecond three-phase transformer, opposite a respective delta apex.

The first three-phase transformer should preferably have third andfourth secondary windings, each having its end connected to that of oneof the first two secondary windings, namely to that which is differentin phase, as well as to a respective secondary winding of the secondthree-phase transformer.

Preferably, the ends of the secondary windings of all phases of thesecond three-phase transformer should be connected to a common neutralpoint, while the beginning of each of these windings should haveconnected thereto the common point of two series-aiding-connectedsecondary windings of the first three-phase transformer, the phase ofthe voltages across the latter windings following that of the voltageacross a respective secondary winding of the second three-phasetransformer, in a preset phase alternation sequence in the powertransmission system.

The herein disclosed phase shifter makes it possible, with its controlwindings shorted, to symmetrically adjust the phase shift between thethree-phase sets of the output voltages at the entry to different linesof a power transmission system of high power-carrying capacity.

The invention will be more fully understood from the following detaileddescription of preferred embodiments thereof with reference to theaccompanying drawings, wherein:

FIGS. 1a, 1b, 1c, 1d, 5a, 5b, 9a, 9b, 13a and 13b, are electric circuitdiagrams of a phase shifter, according to the invention;

FIGS. 2,3,4,6,7,8,10,11,12,14, 15 and 16 are vector diagramsillustrating static states of the phase shifter.

FIG. 17 is an electric circuit diagram of the switching devices.

The proposed phase shifter comprises two three-phase multiwindingtransformers. The primary windings W₁.sub.αA (FIG. 1a-1d) and W₁.sub.βAof phase A, W₁.sub.αB and W₁.sub.βB of phase B, W₁.sub.αC and W₁.sub.βCof phase C of the first (α) and second (β) three-phase transformers,respectively, are series- and star-connected with a common point 0.Applied to beginnings 1 of the primary windings W₁.sub.αA, W₁.sub.βB andW₁.sub.αC of the first transformer α are voltages E_(A), E_(B) and E_(C)from a three-phase power supply. The first three-phase transformer α hassecondary windings W₂.sub.αA, W₂.sub.αB, W₂.sub.αC and W'₂.sub.αA,W'₂.sub.αB, W'₂.sub.αC of phases A, B and C, respectively. The secondthree-phase transformer β has secondary windings W₂.sub.βA, W₂.sub.βBand W₂.sub.βC of phases A, B and C, respectively. The secondary windingsW₂.sub.βA, W₂.sub.βB and W₂.sub.βC of phases A, B and C, respectively,have their ends 2 star-connected with a common point 0'. In thedescription that follows, all winding ends are designated as 2, whileall winding beginnings are designated by 1. Connected to the beginning 1of the secondary winding W'₂.sub.βA of the second transformer β are thebeginnings 1 of the secondary windings W'₂.sub.αB and W₂.sub.αC of thefirst transformer α . Connected to the beginning 1 of the secondarywinding W₂.sub.βB of the second transformer β are the beginning 1 of thesecondary windings W'₂.sub.αC and W₂.sub.αA of the first transformer α .And connected to the beginning 1 of the secondary winding W₂.sub.βC ofthe second transformer β are the beginnings 1 of the secondary windingsW'₂.sub.αA and W₂.sub.αB of the first transformer α. Output voltagesE'_(A), E'_(B), E'_(C) and E"_(A), E"_(B), E"_(C), their sequencestarting from the point 0', form, respectively, two three-phase outputvoltage sets symmetrical with the three-phase power supply. Controlwindings W_(c).sub.αA, W_(c).sub.αB and W_(c).sub.αC FIG. 1c of thefirst transformer α are star-connected and coupled to a switching device3. Control windings W_(c).sub.βA, W_(c).sub.βB and W_(c).sub.βC, FIG.1d, of the second transformer β are also star-connected and coupled to aswitching device 4. It is assumed, in the description of otherembodiments of the phase shifter, that the control windingsW_(c).sub.βA, W_(c).sub.βB, W_(c).sub.βB and W_(c).sub.αA, W_(c).sub.αB,W_(c).sub.αC. are star-connected and coupled to the switching devices 3and 4, respectively.

FIG. 2 is a vector diagram of the output voltages E'_(A), E'_(B), E'_(C)and E"_(A), E"_(B), E" _(C) for the case where the switching devices 3and 4 (FIG. 1) are in the "off" state, i.e. the control windingsW_(c).sub.αA, W_(c).sub.αB, W_(c).sub.αC and W_(c).sub.βA, W_(c).sub.βB,W_(c).sub.βC are disconnected. In the case where all parameters of bothtransformers are similar, the secondary voltages E₂.sub.αA, E₂.sub.αB,E₂.sub.αC and E'₂.sub.αA, E'₂.sub.αB, E'₂.sub.αC (FIG. 2) of the firsttransformer α and E₂.sub.βA, E₂.sub.βB, E₂.sub.βC of the secondtransformer β are equal in magnitude. The output voltages E'_(A),E'_(B), E'_(C) and E"_(A), E"_(B), E"_(C) are found as a result ofgeometric addition of the secondary voltages E₂.sub.αA, E₂.sub.αB,E₂.sub.αC, E'₂.sub.αA, E'₂.sub.αB, E'₂.sub.αC and E₂.sub.βA, E₂.sub.βB,E₂.sub.βC of both transformers in accordance with the followingequations:

    E'.sub.A = E.sub.2.sub.βA + E'.sub.2.sub.αB     1.

    E'.sub.B = E.sub.2.sub.βB + E'.sub.2.sub.αC     2.

    E'.sub.C = E.sub.2.sub.βC + E'.sub.2.sub.αA     3.

    E".sub.A = E.sub.2.sub.βA + E.sub.2.sub.αC      4.

    E".sub.B = E.sub.2.sub.βB + E.sub.2.sub.αA      5.

    E".sub.C = E.sub.2.sub.βC + E.sub.2.sub.αB      6.

the phase angle 1/4 between the output voltages E'_(A) and E"_(A),E'_(B) and e"_(B), E'_(C) and E"_(C) is equal to 60°.

FIGS. 3 and 4 are vector diagrams of the output voltages when the phaseangle θ is equal to 0° or 120°.

Turning now to FIG. 5a, 5b, primary windings W₁.sub.αA and W₁.sub.βA,W₁.sub.αB and W₁.sub.βB, W₁.sub.αC and W₁.sub.βC of the first and secondtransformers α and β, respectively, are connected in a manner similar toFIG. 1a. The secondary windings W₂.sub.βA, W₂.sub.βB and W₂.sub.βC ofthe second transformer β have their ends 2 star-connected with a commonpoint 0'. Connected to the beginning 1 of each secondary windingW₂.sub.βA, W₂.sub.βB and W₂.sub.βC of the second transformer β,respectively, is the common point of two series-aiding-connectedsecondary windings W₂.sub.αB and W'₂.sub.βB, W₂.sub.αC and W'₂.sub.αC,W₂.sub.αA and W'₂.sub.αA of the first transformer α, the phase of thevoltages across these windings following that of the voltage across arespective secondary winding of the second transformer β in a presetphase alternation sequence in the power transmission system.

FIG. 6 is a vector diagram of the output voltages E'_(A), E'_(B), E'_(C)and E"_(A), E"_(B), E"_(C) for the case where the switching devices 3and 4 (FIG. 1) are in the "off" state. If all parameters of bothtransformers are similar, the secondary voltages E₂.sub.αA, E₂.sub.αB,E₂.sub.αC and E'₂.sub.αA, E'₂.sub.αB, E'_(2'C) of the first transformerα and E₂.sub.βA, E₂.sub.βB, E₂.sub.βC of the second transformer β areequal in magnitude. The output voltages E'_(A), E'_(B), E'_(C) andE"_(A), E"_(B), E"_(C) result from geometric addition of the secondaryvoltages of both transformers in accordance with the followingequations:

    E'.sub.A = E.sub.2.sub.βA + E' .sub.2.sub.αB    7.

    E'.sub.B = E.sub.2.sub.βB + E' .sub.2.sub.αC    8.

    E'.sub.C = E.sub.2.sub.βCV + E' .sub.2.sub.αA   9.

    E".sub.A = E.sub.2.sub.βA + E .sub.2.sub.αB     10.

    E".sub.B = E.sub.2.sub.βB + E .sub.2.sub.αC     11.

    E".sub.C = E.sub.2.sub.βC + E .sub.2.sub.αA     12.

the phase angle θ between the output voltages E'_(A) and E"_(A), E'_(B)and E"_(B), E'_(C) and E"_(C) is equal to 90°.

FIGS. 7 and 8 are vector diagrams of the output voltages when the phaseangle θ equals 0° or 180°.

The primary windings W₁.sub.αA and W₁.sub.βA, W₁.sub.αB and W₁.sub.βB,W₁.sub.αC and W₁.sub.βC FIG. 9a of the first and second transformers αand β, respectively, are series- and star-connected. The secondarywindings W₂.sub.βA, W₂.sub.βB and W₂.sub.βC of the second transformer βare delta-connected. Connected to the delta apex opposite the secondarywinding W₂.sub.βC of the second transformer β is the common point of theseries-aiding-connected secondary windings W₂.sub.αC and W'₂.sub.αC ofthe first transformer α. Connected to the apex opposite the secondarywinding W₂.sub.βA of the second transformer β is the common point of theseries-aiding-connected secondary windings W₂.sub.αA and W'₂.sub.αA ofthe first transformer α. And connected to the apex opposite thesecondary winding W₂.sub.βB of the second transformer β is the commonpoint of the series-aiding-connected secondary windings W₂.sub.αB andW'₂.sub.αB of the first transformer α.

FIG. 10 is a vector diagram of the output voltages E'_(A), E'_(B),E'_(C) and E"_(A), E"_(B), E"_(C) for the case where the switchingdevices 3 and 4 are in the "off" state. The parameters of bothtransformers being similar, except for the transformation ratio K.sub.βof the second trasnformer β, which is

     K.sub.β= √ 3.sup.. K.sub.α              13

wherein K.sub.β is the transformation ratio of the first transformer α,the phase angle θ equals 90°.

FIGS. 11 and 12 are vector diagrams of the output voltages for the phaseangle θ equal to 0° and 180°.

The primary windings W₁.sub.αA, W₁.sub.βA, W₁.sub.αB and W₁.sub.βB,W₁.sub.αC, W₁.sub.βC FIG. 13a of the first and second three-phasetransformers α and β, respectively, are connected similarly as shown inFIG. 1a-1d. The secondary windings W₂.sub.βA, W₂.sub.βB and W₂.sub.βChave their ends 2 star-connected with a common point 0'. Coupled to thebeginning 1 of the secondary winding W₂.sub.βA of the second transformerβare those of the secondary windings W'₂.sub.βB and W₂.sub.βC, whileconnected to their ends 2 are those of the secondary windings W"₂.sub.αCand W"₂.sub.αB of the first transformer α. Coupled to the beginning 1 ofthe secondary winding W₂.sub.βB of the second transformer β are those ofthe secondary windings W₂.sub.αA and W'₂.sub.αC, while connected totheir ends 2 are those of the secondary windings W'"₂.sub.αC and W"₂.sub.αA of the first transformer α. And coupled to the beginning 1 ofthe secondary winding W₂.sub.βC of the second transformer β are those ofthe secondary windings W₂.sub.αB and W'₂.sub.αA, while connected totheir ends 2 are those of the secondary windings W"'₂.sub.αA andW"'₂.sub.αB of the first transformer α. The control windings of bothtransformers are connected to switching devices as shown in FIG. 1a andFIG. 1d.

FIG. 14 is a vector diagram of the output voltage E'_(A), E'_(B), E'_(C)and E"_(A) , and E" _(B), E"_(C) for the case where the switchingdevices 3 and 4 are in the "off" state. The phase angle θ between theoutput voltages E'_(A) and A"_(A), E'_(B) and E"_(B), E' _(C) and E"_(C)is equal to 90° just as in the previous embodiment.

FIGS. 15 and 16 are vector diagrams of the output voltages for the phaseangle θ equal to 0° and 180°.

FIG. 17 is a schematic of the switching device 3 and its connection tothe control windings W_(c).sub.αA, W_(c).sub.αB and W_(c).sub.αC of thefirst transformer α. The switching device 4 and its connection to thecontrol windings of the second transformer β are similar to those of theswitching device 3.

Used as the switching device 3 are two full-wave static a-x switches 5and 6. The full-wave static switch 5 has two series connected thyristors7 and 8 placed in parallel wherewith are two series-opposing-connecteddiodes 9 and 10. A point 11 of connection of the thyristors 7 and 8 isconnected to a point 12 of connection of the diodes 9 and 10, bothpoints being also connected to the negative terminal of a control signalsource. The control electrodes of the thyristors 7 and 8 are coupled,via resistors 13 and 14, to the positive terminal of the control signalsource. A point 15 of connection is coupled to the control windingW_(c).sub.αA, while a point 16 of connection is coupled to the controlwinding W_(c).sub.αC. The second full-wave static switch 6 is similar tothe switch 5 and connected to the control windings W_(c).sub.αA andW_(c).sub.αB. As the switching devices 3 and 4 use can also be made ofpower contact switches. The switching devices 3 and 4 can be connecteddirectly in parallel with the primary windings W₁.sub.αA, W₁.sub.αB,W₁.sub.αC and W₁.sub.βA, W₁.sub.βB, W₁.sub.βC of the first and secondthree-phase transformers, respectively.

Consider now two modes of operation of the phase shifter with one of theswitching devices 3 and 4 being in the "on" state. In the first mode ofoperation, it is the switching device 3 (FIG. 1c) that is in the "on"state, whereas the switching device 4 is in the "off" state. As acontrol signal is applied to the control electrodes of the thyristors 7and 8 (FIG. 17), the latter are rendered conducting; the thyristor 7 anddiode 10 being conducting during the positive half-cycle, and thethyristor 8 and diode 9 being conducting during the negative half-cycle.The full-wave static switch 6 operates in a similar manner, therefore,the control windings W_(c).sub.αA, W_(c).sub.αB and W_(c).sub.αC of thefirst transformer become shorted. As a result, the voltages E_(A) E_(B)and E_(C) (FIGS. 1a, 5a, 9a and 13a) are practically fully applied tothe primary windings W₁.sub.βA, W₁.sub.βB and W₁.sub.βC of the secondtransformer β which carries all of the load. The voltages a cross theprimary windings W₁.sub.αA, W₁.sub.αB, W₁.sub.αC and all the secondarywindings of the first transformer are close to zero and the phase angleθ (FIGS. 3,7, 11 and 15) between the output voltages E'_(A) and E"_(A),E'_(B) and E"_(B), E'_(C) and E"_(C) approximates zero, too. This modeof operation is recommended for no-load or low load conditions in a-cpower transmission lines of high power-carrying capacity. In this case,the power of the second transformer is approximately equal to half themaximum load.

The second mode of operation is characterized by the switching device 4(FIGS. 1d) being in the "on" state and the switching device 3 being inthe "off" state. In this case, the control windings W_(c).sub.βA,W_(c).sub.βB and W_(c).sub.βC of the second transformer β becomeshorted. As a result, the voltages E_(A), E_(B) and E_(C) arepractically fully applied to the primary windings W₁.sub.αA, W₁.sub.βBand W₁.sub.βC of the first transformer α which carries all of the load.The voltages across the primary windings W₁.sub.βA, W₁.sub.βB, W₁.sub.βCand secondary windings W₂.sub.βA, W₂.sub.βB, W₂.sub.βC of the secondtransformer β approach zero. The phase angle θ between the outputvoltages E'_(A) and E"_(A), E'_(B) and E"_(B), E'_(C) and E"_(C) may inthis case be equal to 120° (FIG. 4) or 180° (FIGS. 8, 12 and 16). Thismode of operation is recommended for high load conditions prevailing ina-c power transmission lines of high power-carrying capacity.

Since the power of the first transformer α is equal to the maximum loadcapacity and the power of the second transformer β is equal to half themaximum load capacity, the installed power of the phase shifter equalsone and a half of the maximum load capacity. In addition, the use in thephase shifter of two series-connected transformers α and β substantiallyreduces the longitudinal resistance introduced into the load circuit.

Thus, the herein disclosed phase shifter makes it possible, depending onthe load and with the control windings of one of the transformersshorted, to switch over a power transmission system of highpower-carrying capacity from operation with the phase angle θ betweenthe voltages of the entry to adjacent lines being equal to 0° tooperation with the phase angle being equal to 120° or 180°.

What is claimed is:
 1. A phase shifter comprising three-phasemultiwinding transformers, each of said transformers having primarywindings connected in series with respect to like phases and arranged ina three-phase system, and having secondary windings and controlwindings, a first three-phase transformer having other secondarywindings connected to said secondary windings of the first transformer,said secondary windings being arranged in a three-phase system,switching devices, the control windings of each three-phase transformerbeing connected to respective switching devices, the beginnings of thetwo secondary windings of the two other phases of the first three-phasetransformer being connected to the beginnings of the secondary windingsof each phase of the second transformer, the ends of said secondarywindings of each phase of the second transformer being connected to acommon neutral point.
 2. A phase shifter in accordance with claim 1,wherein said first three-phase transformer has third and fourthsecondary windings, the end of each winding being connected to the endof one of the first two secondary windings differing in phase, as wellas to a respective secondary winding of said second three-phasetransformer.
 3. A phase shifter in accordance with claim 1, wherein thebeginning of each secondary winding of the second three-phasetransformer is connected to the common point of twoseries-aiding-connected secondary windings of said first three phasetransformer, the phase of the voltages thereacross following that of thevoltage across a respective secondary winding of said second three-phasetransformer in a preset phase alternation sequence in a powertransmission system.
 4. A phase shifter in accordance with claim 1,wherein secondary windings of said second three-phase transformer aredelta-connected, each delta apex having connected thereto said commonpoint of a pair of series-aiding-connected secondary windings of saidfirst three-phase transformer, the phase of the voltages across eachsaid pair of series-aiding-connected secondary windings of said firstthree-phase transformer coinciding with that of the voltage across saidsecondary winding of said second three-phase transformer opposite arespective delta apex.